Pwm method and apparatus, and light source driven thereby

Abstract

The present invention provides a pulse-width modulation (PWM) method and apparatus, and light source driven thereby. In particular, the present invention provides a PWM method and apparatus for generating a PWM signal having a desired resolution and frequency using generating means traditionally limited to providing PWM signals having a lower resolution and/or frequency. The PWM method and apparatus of the present invention may be used in a number of applications where a relatively high PWM resolution and/or frequency is desired, but where selection of generating means for generating such PWM signals is relatively limited by cost and/or other such constraints. For example, a PWM signal generated by the method and apparatus of the present invention may be useful in accurately controlling the output of the one or more light-emitting elements of a light source, namely to control a dimming and/or colour level thereof, without using driving components that may be relatively costly for the application at hand.

1 . An apparatus for generating a PWM signal having a desired resolution and frequency, the apparatus comprising:
 a generating module for generating a first PWM signal having the desired resolution; and   a comparing module adapted to compare said first PWM signal to a reference signal indicative of the desired frequency and thereby generate a second PWM signal substantially having the desired resolution and frequency.   
     
     
         2 . The apparatus as claimed in  claim 1 , further comprising a converting module for converting said first PWM signal into an intermediate signal indicative of the duty cycle of said first PWM signal, said comparing module adapted to compare said intermediate signal to said reference signal and thereby generate said second PWM signal. 
     
     
         3 . The apparatus as claimed in  claim 2 , wherein said intermediate signal comprises an analog signal, said comparing module adapted to compare said analog signal to said reference signal. 
     
     
         4 . The apparatus as claimed in  claim 1 , wherein said generating module comprises one or more of a microcontroller, a processor, a digital processor, a field programmable gate array, a counter, a timer and an operational amplifier. 
     
     
         5 . The apparatus as claimed in  claim 2 , wherein said converting module comprises one or more of a digital to analog converter, a band pass filter, a notch filter and a low pass filter. 
     
     
         6 . The apparatus as claimed in  claim 5 , wherein said converting module comprises a low pass filter, said low pass filter comprising one or more of a passive first order filter, an active first order filter, a passive higher order filter and an active higher order filter. 
     
     
         7 . The apparatus as claimed in  claim 1 , wherein said comparing module comprises one or more of a comparator, an operational amplifier, a Schmitt trigger and a phase-lock loop. 
     
     
         8 . The apparatus as claimed in  claim 7 , wherein said comparing module comprises a high speed comparator. 
     
     
         9 . The apparatus as claimed in  claim 3 , wherein said reference signal is selected from the group comprising a triangle signal and a saw-tooth signal. 
     
     
         10 . The apparatus as claimed in  claim 3 , for generating two or more simultaneous PWM signals having the desired resolution and frequency, said generating module for generating two or more simultaneous first PWM signals, said converting module for converting each of said simultaneous first PWM signals into respective analog signals, and said comparing module adapted to compare said respective analog signals to one or more reference signals and thereby generate respective simultaneous second PWM signals having the desired resolution and frequency. 
     
     
         11 . The apparatus as claimed in  claim 10 , said comparing module adapted to compare said respective analog signals to respective reference signals configured to impart one or more respective signal characteristics to each of said respective simultaneous second PWM signals. 
     
     
         12 . The apparatus as claimed in  claim 11 , wherein said one or more respective signal characteristics comprise one or more of a frequency, a phase and a modulation. 
     
     
         13 . The apparatus as claimed in  claim 1  for use in generating a driving signal for driving one or more light-emitting elements of a light source. 
     
     
         14 . A method of generating a PWM signal having a desired frequency and resolution, the method comprising the steps of:
 generating a first PWM signal having the desired resolution; and   comparing said first PWM signal to a reference signal indicative of the desired frequency to generate a second PWM signal substantially having the desired frequency and resolution.   
     
     
         15 . The method as claimed in  claim 14  further comprising the step of converting said first PWM signal into an analog signal indicative of the duty cycle of said first PWM signal, said comparing step comprising comparing said analog signal to said reference signal to generate said second PWM signal. 
     
     
         16 . The method as claimed in  claim 15 , for generating two or more simultaneous PWM signals, said generating step comprising generating two or more simultaneous first PWM signals, said converting step comprising converting each of said simultaneous first PWM signals into respective analog signals, and said comparing step comprising comparing each of said respective analog signals with one or more reference signals to generate respective simultaneous second PWM signals having the desired resolution and frequency. 
     
     
         17 . A light source comprising:
 one or more light-emitting elements; and   a driving system for driving each one of said one or more light-emitting elements at a given frequency and at a respective relative intensity, said driving system comprising:
 a generating module for generating, for each of said one or more light-emitting elements, a first PWM signal having a duty-cycle indicative of said respective relative intensity; and 
 a comparing module adapted to compare each said first PWM signal to a reference signal indicative of said given frequency and thereby generate a respective second PWM signal at said given frequency conducive to driving a respective one of said one or more light-emitting elements at said respective relative intensity. 
   
     
     
         18 . The light source as claimed in  claim 17 , said driving system further comprising a converting module for converting each said first PMW signal into an analog signal indicative of said duty-cycle thereof, said comparing module adapted to compare each said analog signal to said reference signal to generate said respective second PWM signal. 
     
     
         19 . The light source as claimed in  claim 18  comprising two or more light-emitting elements, said comparing module adapted to compare each said analog signal to a respective reference signal configured to impart one or more respective signal characteristics to said respective second PWM signal conducive to driving said respective one of said one or more light-emitting elements in accordance therewith. 
     
     
         20 . The light source as claimed in  claim 19 , wherein said one or more respective signal characteristics comprise one or more of a frequency, a phase and a modulation. 
     
     
         21 . The light source as claimed in  claim 20 , said one or more respective signal characteristics comprising a respective phase such that a load applied to a power supply of the light source is distributed over a period of said respective second PWM signals. 
     
     
         22 . The light source as claimed in  claim 21 , wherein said one or more respective signal characteristics further comprise a respective modulation, which provides for a communication of information using said two or more light-emitting elements, and wherein said respective phase provides for a substantially continuous signal to be communicated via said two or more light-emitting elements. 
     
     
         23 . The light source as claimed in  claim 17 , said generating module for generating each said first PWM signal with a desired resolution providing a desired level of control on each said respective relative intensity. 
     
     
         24 . The light source as claimed in  claim 23 , wherein said desired level of control is determined as a function of a desired dimming control over each said respective relative intensity. 
     
     
         25 . The light source as claimed in  claim 23  comprising two or more light-emitting elements having respective spectral outputs, wherein said desired level of control is determined as a function of a desired relative intensity control between said two or more light-emitting elements conducive to providing a controlled combined spectral output. 
     
     
         26 . The light source as claimed in  claim 25 , wherein said combined spectral output comprises one or more of: a selected white light, a selected coloured light, a selected chromaticity, a selected colour rendering index, a selected colour quality scale, a selected output efficiency, a selected luminance and a selected colour temperature. 
     
     
         27 . The light source as claimed in  claim 25 , wherein said desired level of control is further determined as a function of a desired dimming control. 
     
     
         28 . The light source as claimed in  claim 17 , said comparing module comprising a phase-lock loop, wherein said reference signal is provided as a function of an output of said phase-lock loop.